Through the passage of the Communications Assistance for Law Enforcement Act of 1994 (CALEA), 47 U.S.C. §§ 1001-1010, the United States has mandated that telecommunications carriers provide law enforcement agencies with access to the telecommunications networks to enable lawfully-ordered intercept of the voice content of telecommunications. Industry standards such as Lawfully Authorized Electronic Surveillance (ANSI-J-STD-025A), incorporated by reference herein, provide a framework for achieving this goal.
When a person involved in a call has been identified as an intercept subject, i.e., the person under law enforcement surveillance, one or more law enforcement agencies may seek to obtain the call content transmitted and received by that person. In a traditional public switched telephone network (“PSTN”), this is a reasonably straightforward undertaking. There, the bearer path (or paths) of calls are routed through fixed points for the duration of the call. To intercept the call content, all that is usually required is access to one of these fixed points.
By contrast, the interception of the transmitted and received call content in a soft switch environment presents certain challenges not encountered in the traditional network. Under the soft switch scheme, the call content travels along bearer paths that may be reconfigured during the course of a call and, hence, the paths themselves may be routed through different points over the course of that call. Thus, while a desired component of the call content may be passing through a given point at the outset of a call, after reconfiguration it may no longer be accessible from that point. For example, this may occur when telephone calls are handed off in transfers and forwarded calls. Therefore, one access point will not necessarily provide access to the transmitted and received call content for the duration of the call.
The difficulties discussed above may be overcome in part by selecting access points in the telecommunications system from which to obtain the various components of the call content, namely, the intercept subject's transmitted call content and the call content received (or that could be received) by the intercept subject from other parties to a call. Since the call content transmitted and received by the intercept subject must pass through some point in the telecommunications system, any point within the system will suffice for access to that component, provided that it passes through that point irrespective of any reconfiguration of the bearer path. Another criteria is that the device be capable of receiving and responding to instructions from the soft switch. One type of device where a call component may be obtained is a network device controlled by a soft switch, at or near the periphery of the network where the call content enters or passes into the network. Examples of network devices include access gateways, media gateways, network edge devices, trunk gateways, and border elements, although this list is not exclusive.
In some telecommunications systems, however, there is no convenient network device such as a gateway that will provide an access point for an unobtrusive interception. Rather, the subscriber or participant connects directly to the network through an access device on its premises and therefore interception of call content at such points might be detected by the intercept subject. In such a case, a soft switch-controlled network device through which a subscriber connects, such as an ATM switch, an edge router, or another border element, may provide a point for interception of a call content component.